The document EP-A-0 631 901 describes various examples of such irreversible adjustment mechanisms.
Mechanisms of this type enable continuous adjustment of a component driven by the output part by carrying out one or more alternating "pumping" movements:
For example, such mechanisms can be used in particular to adjust the height of the seat part of a vehicle seat.
These known mechanisms taken as a whole give satisfaction, but however have the disadvantage that, when the input part pivots in one of the angular directions from its neutral position, the output part is itself only driven after a certain dead angular travel which is random (this dead angular travel can have for example a maximum value of 9 degrees, and vary randomly between 5 and 9 degrees under load).
This random variation of the dead angular travel is due to the fact that the positioning of the first and second stop surfaces relative to the first and second clamping bodies is itself random, in view of: